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Vital capacity

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Vital capacity

Output of a spirometer

Vital capacity is the maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.

A person's vital capacity can be measured by a wet or regular spirometer. In combination with other physiological measurements, the vital capacity can help make a diagnosis of underlying lung disease. Furthermore, the vital capacity is used to determine the severity of respiratory muscle involvement in neuromuscular disease, and can guide treatment decisions in Guillain-Barré syndrome and myasthenic crisis.

A normal adult has a vital capacity between 3 and 5 litres.[1] A human's vital capacity depends on age, sex, height, mass, and ethnicity.[2]

Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle. Lung volumes are directly measured, whereas lung capacities are inferred from volumes.


Role in Diagnosis

The vital capacity can be used to help differentiate causes of lung disease. In restrictive lung disease the vital capacity is decreased. In obstructive lung disease it is usually normal or only slightly decreased.[3]

Estimated vital capacities

Males by height[4]:182
Height 150–155 cm (5'–5'2") 155–160 cm (5'2"–5'4") 160–165 cm (5'4"–5'6") 165–170 cm (5'6"–5'8") 170–175 cm (5'8"–5'10") 175–180 cm (5'10"–6')
Vital capacity (cm3) 2900 3150 3400 3720 3950 4300
Males by age[4]:183
Age 15–25 25–35 35–45 45–55 55–65
Vital capacity (cm3) 3425 3500 3225 3050 2850

Formulas

Vital capacity increases with height and decreases with age. Formulas to estimate vital capacity are:[1]

\begin{align} vc_{female} = (21.78 - 0.101 a ) \cdot h \\ vc_{male} = (27.63 - 0.112 a ) \cdot h \\ \end{align}


where vc is approximate vital capacity in cm3, a is age in years, and h is height in cm.

References

  1. ^ a b "Vital Capacity". Family Practice Notebook. 
  2. ^ Hutchinson, J (1846). "On the capacity of the lungs, and on the respiratory functions, with a view of establishing a precise and easy method of detecting disease by the spirometer". Med Chir Trans 29: 137–252.  
  3. ^ "Pulmonary Function Tests". UCSD. Retrieved 21 November 2014. 
  4. ^ a b Pratt, Joseph H. (1922). "Long-continued observations on the vital capacity in health and in heart disease". Transactions of the Association of American Physicians (W. J. Dornan, Incorporated) 37: 182–197. 

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